A • Brown tipping on leaves is typically a sign of an environmental or abiotic issue, rather than an insect or disease. It could have been caused by the plant becoming too dry over a certain period, by being exposed to cold during the winter months or by getting too much fertilizer.
However, one of the other possible explanations is that the browning is a symptom of fluoride toxicity. Many municipalities will add fluoride to the water supply to help prevent tooth decay. When plants are watered with fluoridated water, fluoride is translocated into the leaves, where it can accumulate in the tips over time. If levels in the leaf become high enough, it will cause injury in the form of necrotic leaf tips.
Dracaenas, Easter and peace lilies, spider plants and prayer plants are all sensitive to fluoride. To prevent this damage, avoid using fluoridated water on sensitive plants, and opt for bottled, distilled or rainwater instead. The brown tips can be trimmed off, as they will not become green again. Also, ensure that plants are properly watered and fertilized at the correct rates.
Write to the Missouri Botanical Garden’s Center for Home Gardening at firstname.lastname@example.org or the Horticulture Answer Service, 4344 Shaw Blvd., St. Louis, MO 63110.